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Cobb, KM, Charles CD, Cheng H, Edwards RL.  2003.  El Nino/Southern Oscillation and tropical Pacific climate during the last millennium. Nature. 424:271-276.   10.1038/nature01779   AbstractWebsite

Any assessment of future climate change requires knowledge of the full range of natural variability in the El Nino/Southern Oscillation (ENSO) phenomenon. Here we splice together fossil-coral oxygen isotopic records from Palmyra Island in the tropical Pacific Ocean to provide 30-150-year windows of tropical Pacific climate variability within the last 1,100 years. The records indicate mean climate conditions in the central tropical Pacific ranging from relatively cool and dry during the tenth century to increasingly warmer and wetter climate in the twentieth century. But the corals also document a broad range of ENSO behaviour that correlates poorly with these estimates of mean climate. The most intense ENSO activity within the reconstruction occurred during the mid-seventeenth century. Taken together, the coral data imply that the majority of ENSO variability over the last millennium may have arisen from dynamics internal to the ENSO system itself.

Fairbanks, RG, Evans MN, Rubenstone JL, Mortlock RA, Broad K, Moore MD, Charles CD.  1997.  Evaluating climate indices and their geochemical proxies measured in corals. Coral Reefs. 16:S93-S100.   10.1007/s003380050245   AbstractWebsite

Standard ocean/climate indices such as the Nino-3 sea surface temperature (SST) index, based on sparse instrumental data, and atmospheric indices such as the Southern Oscillation Index (SOI), may now be substituted and/or extended by coral-based indices. Several elements or their isotopes are incorporated in coral aragonitic skeletons at predictable concentrations, some of which are temperature or salinity dependent. The availability of century-old corals, at key oceanographic sites, permits the establishment of a network of proxy climate indices.

Mortlock, RA, Charles CD, Froelich PN, Zibello MA, Saltzman J, Hays JD, Burckle LH.  1991.  Evidence for Lower Productivity in the Antarctic Ocean During the Last Glaciation. Nature. 351:220-223.   10.1038/351220a0   AbstractWebsite

BOTH increased biological productivity and more efficient uptake of upwelled nutrients in high-latitude oceans have been proposed 1-5 as mechanisms responsible for the glacial reduction in atmospheric concentrations of carbon dioxide deduced from ice-core measurements 6-8. These glacial models invoke more efficient 'biological pumping' of carbon into the deep sea by increasing the uptake of 'excess' biolimiting nutrients in the Antarctic surface ocean 9 or by reorganizing chemical circulation patterns within the ocean 10,11. Here we challenge this conventional view with new evidence from tracers of palaeoproductivity preserved in Antarctic sediments. Records of the accumulation rates of diatom shells, the ratio of germanium to silicon in diatomaceous opal and the carbon isotope ratio in foraminiferal carbonate all suggest lower glacial productivity and less efficient uptake of nutrients. Although alternative interpretations are possible, our results support previous studies that indicate lower glacial productivity in the Southern Ocean 12,13 and raise new questions about the role of ocean productivity in models of the causes (or remedies) for changes in atmospheric concentrations of carbon dioxide.

Charles, CD, Fairbanks RG.  1992.  Evidence From Southern-Ocean Sediments for the Effect of North-Atlantic Deep-Water Flux on Climate. Nature. 355:416-419.   10.1038/355416a0   AbstractWebsite

The Southern Ocean is perhaps the only region where fluctuations in the global influence of North Atlantic Deep Water (NADW) can be monitored unambiguously in single deep-sea cores. A carbon isotope record from benthic foraminifera in a Southern Ocean core reveals large and rapid changes in the flux of NADW during the last deglaciation, and an abrupt increase in the NADW production rate which immediately preceded large-scale melting of the Northern Hemisphere ice sheets. This sudden strengthening of the NADW thermohaline cell provides strong evidence for the importance of NADW in glacial-interglacial climate change.